Psychiatric comorbidity is a major concern for adolescents with substance use or psychiatric disorders. Eighty-five percent of adolescents in treatment for a substance use disorder have an additional psychiatric comorbidity. Similarly, psychiatric disorders have an important role in the etiology of and vulnerability to substance use disorders. Adolescents with both mental and substance disorders are more persistent, severe, and treatment resistant than patients with pure disorders, have more behavioral and medical problems, and higher suicide risk. While effective treatments exist for adolescents with comorbid substance and psychiatric disorders, clinicians fail to identify the comorbid psychiatric condition 65% of the time (the detection rate was as low as 5% in fee for service systems). SAMHSA's Blueprint for Action calls increased screening of comorbidity a national priority. The current study will develop an on-line, computerized screening tool to identify comorbid psychiatric disorders in adolescents with substance use or psychiatric disorders. The tool, based on the KSADS, will also contain embedded severity scales to monitor change over time. Computerization facilitates accessibility, enabling wider dissemination, especially when clinician-diagnosticians are unavailable. Fifty adolescents and their parents will take computer and clinician versions of the interview in counterbalanced order; ancillary scales will evaluate construct validity. The study will generate data on reliability, validity, feasibility, clinical utility, user satisfaction, and equivalence to clinician administered diagnosis. PUBLIC HEALTH RELEVANCE: Comorbid substance abuse and psychiatric disorders in adolescents has been identified as a major public health issue. Failure to identify the comorbidity is common, and results in significantly worse treatment outcomes for patients and greater burden on society. A web-based screening device will help facilitate detection and treatment of comorbidity, resulting in more effective treatment outcomes for patients and decreased societal burden.